By David Savastano, Ink World Editor

To be successful in any industry, equipment manufacturers must have a strong insight into what their customers are developing. Ink makers know what printers are looking for, and they are tailoring their inks to meet these demands.

In recent years, the two strongest growth areas in the printing ink industry are energy-curing ultraviolet (UV) and electron beam (EB) inks and ink jet and digital inks.

The need to tailor products to the newest innovations of their customers also holds true for equipment manufacturers, and mill companies are doing just that for ink manufacturers. In terms of milling requirements, ink jet inks are on the opposite end of the spectrum from energy-cured inks. Where UV inks tend to be high viscosity, ink jet inks have to be low viscosity with fine particle distribution, through necessity: these inks have to fit through a print head.

Meanwhile, more mainstream ink manufacturers are facing their own requirements from printers, which in turn leads to necessary improvements in milling equipment. As such, ink companies are working with their milling counterparts to develop new products.

As a result, there are many new changes in the works that should lead to even better results for ink makers in the future.

Mills for Ink Jet Inks
As noted above, the two major areas of growth within the printing ink industry are ink jet inks and UV/EB inks. Ink jet and digital inks are the fastest-growing segment of the ink industry, with estimates placing the growth at better than 20 percent annually.

Considering the improvements being made in ink jet technology and the gains being made in digital presses, it is clear that ink jet inks are on the rise.

“Digital inks and e-inks are a growing industry,” said Wendy Rogalinski, MFIC Corporation’s marketing communications manager, “and our customers are becoming ever more demanding so they can stay ahead of their competition.”

In order to be effective, ink jet inks are low viscosity and fine particle size. Milling manufacturers are working to meet those two requirements.

“Ink jet inks are very low in viscosity and require a high degree of fineness to pass through the nozzle,” said Kirsten Grosse, sales manager, grinding and dispersion group for Buhler Inc. “Usually these inks require a narrow particle distribution.”

John Sneeringer, technical director of Premier Mill, said he is also seeing an interest in digital printing. Many new formulations are being developed in the low to medium viscosity range. This fits well with Premier’s Supermills and Submersibles basket mills, which are most efficient in this range.

“We’re seeing a trend toward finer particle size and more narrow particle distribution requirements for applications such as ink jet inks,” Mr. Sneeringer said. “Our customers also want to use finer grinding media as small as 0.1 mm., not just in inks, but also in other applications such as automotive coatings and conductive ceramic applications.”

“Our Morehouse-Cowles division manufactures dispersers and media mills that can reduce particles sizes to 1 micron,” Ms. Rogalinski said. “For more demanding digital and e-ink applications, our Microfluidics division manufactures Microfluidizer Processors which produce submicron particle sizes for pigmented and dye type inks. With these processors, all of the ink is forced through the ‘interaction chamber’ which has a diameter smaller than a human hair, and all the ink particles are subject to shear and impact. This unique technology means Microfluidics is listed in a lot of patents because our equipment allows our customers to create products they couldn’t otherwise without our equipment.”

“In the ink jet market, Netzsch is the leader in terms of process knowledge,” said Harry Way, manager of research and development for the grinding and dispersion division of Netzsch Incorporated. “The patented Netzsch media separation system easily allows use of grinding media smaller than 200 microns. Netzsch’s experience in this market has optimized materials of construction for metal free grinding; process control with the Voyager control system results in minimal downtime and process repeatability. The broad pallet of machines in the Netzsch product line allows tailoring of the correct premixing and grinding systems for each product rheology.”

“With a standard spike mill and small-sized ceramic media, we’ve been able to successfully achieve submicron size,” said Gerry Chait, vice president and COO of Inoue USA.

The Sweet Side of Milling

Not many people would discuss printing ink and chocolate in the same sentence. However, the two do share one similarity: both chocolate and printing inks are put through similar mills.

Buhler Inc. is one such company that serves both the printing ink and chocolate industries; in fact, the company used to have a single division dedicated to both fields.

“In former times, we had a chocolate and ink division, but it was reorganized,” said Kirsten Grosse, sales manager, grinding & dispersion group for Buhler Inc. “The chocolate division went to the process food division and inks went to the process technologies division.”

There are similarities and differences between the needs of the two industries. Like ink, chocolate comes in practically countless varieties. “There are hundreds of types of cocoa products ranging from chocolates to glazes, all of which use different formulations and processes,” said Stanley Goldberg, director of Glen Mills, Inc., a grinding media specialist which also distributes Dyno-Mills, which can be used to grind chocolates or pigments.

In the case of chocolates, the optimal size for cocoa particles is approximately 12 microns. “Your tongue has the ability to feel texture,” Mr. Goldberg said. “If the particles are too big, say 20 to 75 microns, then your tongue would sense an unpleasant roughness. If the particles are too small, say 1 to 9 microns, the cocoa particles would bind up more of the expensive cocoa butter. This would add cost to the process for more butter would have to be added to keep the product fluid.”

“The bead mills used for cocoa mass are very similar to those used in the ink industry,” Ms. Grosse said. “They are vertical bead mills, but they use larger beads because the particles are much larger. Our customers typically use 6.3mm beads for cocoa mass. Inks use smaller beads.”

Bead selection is also somewhat different for chocolate for reasons that become obvious; while inks can use steel or ceramic beads, chocolate manufacturers stay strictly with steel media. “Chocolate companies use steel beads, as they are magnetic and can be filtered out,” Ms. Grosse said.

“Chocolate is very viscous, and chocolate companies usually use steel balls because of density, reasonable cost and lack of wear,” Mr. Goldberg said.

Energy-Cured Inks In the 1960s, UV inks were just an idea in the minds of some innovative ink leaders. For the next few decades, the growth of UV printing was limited.

However, dramatic improvements in UV formulations and the environmental advantages of UV printing have made energy-cured inks a strong growth area for the past few years. Ink sales have experienced double-digit growth annually during this period, and as demand for these inks grows, competition is increasing.

As a result, ink manufacturers are looking to improve their products, and equipment plays a significant role. A number of milling companies are working on new equipment to produce these high-viscosity inks.

“When we approach ink companies, they tell us they would like to develop certain processes, which is how we like to work since we really don’t have an off-the-shelf unit,” said Mr. Chait. “We’ve been testing on UV inks with a high degree of success, and we are looking into the future for what our customers will need. The expanded version of our Spike Mill is designed to handle UV and other inks of high viscosity, and handle varying degrees of viscosities of paste and liquid.”

While ink jet inks are low viscosity, UV and EB inks are quite the opposite.

“UV inks have a high-end viscosity and are very temperature sensitive. They can only achieve good curing properties when low temperature limits are maintained,” Ms. Grosse said. “Typically, three roll mills were used for UV inks because bead mills created an uncontrolled thermal reaction which could lead to polymerization,” Ms. Grosse said. “However, a bead mill gives a better grind than a three roll mill, because some pigments, such as certain violets, greens and magentas, are more difficult to disperse. Our K series mills, with their conical grind chambers, have larger cooling areas which allow them to process these inks.”

As such, the traditional three roll mills cannot achieve the fineness necessary for low viscosity products, but used in tandem with other mills, will help create the necessary properties for the inks while only going through a single pass.

“We are still using three roll mills, but we place them after the bead mills, which helps the inks achieve a little better gloss and color strength,” Ms. Grosse said. “It still remains a one-pass operation.”

“Netzsch addressed the UV market with the introduction of the NKM or ‘Inka’ grinding mill,” said Mr. Way. “This mill is based on the well known Netzsch John mill but has been optimized for temperature control, media separation and cleaning. The machine was introduced in May 2000 at the Achema in Frankfurt, Germany, and has already been successfully installed in the UV market for paste inks in Europe.”

Other Trends Not all of the growth in the printing ink industry is related to energy-cured and ink jet inks. Other ink systems have their own unique requirements, and milling manufacturers are working to meet these needs.

“Netzsch is supplying more and more automated production systems or turnkey systems,” Mr. Way said. “These total system designs include automated premixing, grinding and de-aeration, whether it is circulation process for liquid inks or continuous process for paste inks.”

“The demand for higher efficiency is always pushing us. Every customer wants to get more gallons per hour from their mills,” Mr. Sneeringer said.

“Ink manufacturers are looking to streamline and produce the highest quality products,” said Todd Kritzer, sales manager at Kady International. “They are doing this by ‘premilling’ rather than premixing upstream to their media mills.”

Working with Customers There are many cases where an ink manufacturer has a unique project with its own specifications. If that is the case, milling companies will work to see that these needs are met.

“Netzsch has always been a leader in customer and technical service,” Mr. Way said. “With the consolidation in industry, Netzsch continuously expands their global operations so that the service and support for operations established in one market can be easily duplicated with the same machines supplied locally and the same level of support in operations around the world. In the North American market, Netzsch maintains a staff of service engineers and technicians unmatched by any other manufacturer. Netzsch understands the need for manufacturers to outsource service and maintenance and has met this challenge by continuously expanding its service and support staff and increasing domestic spare parts supply. The construction of a new 14,000 square feet laboratory and technical center for customer testing and training is the latest step Netzsch has taken in maintaining its position in this market.”

New Products To help meet the increasing requirements for new products, printing ink formulators are studying new developments in milling technology.

In order to create the fineness needed for ink jet inks, Buhler introduced its ZR120 bead mill in Europe last year, and is bringing it to the U.S. this year.

“The ZR120 targets low viscosity products that require a fineness in the sub-micron area,” said Ms. Grosse. “The grinding media has to be extremely small, and a ZR120 uses 0.2mm to 0.8mm beads. This allows us to get that fineness more efficiently.”

“In terms of total process systems, the latest concepts for paste and UV inks from Netzsch are the HVS (hydraulic) premixing with sublevel vacuum pigment feeding, grinding with the new NKM mill and polishing with the new Three Roll Mills,” Mr. Way said. “This entire process can then be finished with Netzsch filling systems.”

“We have developed high energy grinding configurations and are working on a new line of recirculation milling systems which will be available soon,” said Mr. Sneeringer of Premier Mill. “We believe these new high energy configurations will have a big impact. One new product that is generating great interest is our new Submersible Mill, which fits customers who need to run smaller special batches and make numerous color changes.”

MFIC is offering the M-140K laboratory Microfluidizer Processor, which is capable of processing at pressures up to 40,000 psi, and is one of Microfluidics’ more popular processors for ink/digital ink applications. Scaleup is guaranteed to production volumes.

“Many high speed dispersers are being replaced by Kady Mills,” Mr. Kritzer said. “Kady produces a much finer mill base, resulting in fewer mill passes and better color development. Many times, in a one pass process, the Kady Mill is able to eliminate milling altogether.”

“Our new continuous Kady is an in-line throughput type machine,” Mr. Kritzer added. “This machine can easily be plumbed in-line or in a recirculation loop with a conventional premix device. This Kady will also enhance a premix and improve milling throughput.”

Union Process, inventors and developers of Attritor technology, is offering its new circulation QC-Mill for super fine grinding. The specially designed rotor of this small media mill creates strong centrifugal and shearing forces inside the mill. These forces, combined with the fast circulation rate of the slurry, result in excellent and efficient grinding with sharp particle size distribution.

The QC-Mill requires less energy due to the small amount of media required. In addition, the mill’s simple design makes it easy to disassemble and clean. Additives may be added during operation for convenience. Finally, since the mill uses a circulation process, a large batch can be made with minimal personnel costs. Available in six different models, the QC-Mill can handle batches ranging from one gallon to 400 gallons.

Inoue USA is offering its Spike Mill, which is a continuous annular-stirred, wet media bead mill with a unique plug-flow movement which enables it to meet high industry tolerances for finer particle size reduction and dispersion. The Spike Mill is available in various sizes, and performs its functions with less residence time than conventional bead mills. With its cylindrical rotor, it evenly distributes grinding energy for more efficiency and greater effectiveness while maintaining cooling efficiency.

Draiswerke’s new ViscoFlow Perl Mill has been specifically developed for the intensive grinding of temperature sensitive products, and formulations of highest viscosities, such as UV curable inks, can be processed to superior qualities with the highest economic efficiency.

The ViscoFlow Perl Mill features a narrow, ring-cylindrical process vessel on a particularly large diameter, and the rotor and the stator provide for high-intensity cooling. As the clearance between the pegs decreases continuously, the shear intensity increases in the flow direction. The specific peg arrangement results in a homogenous distribution of grinding media even with the highest viscosities.

As time passes on, it is reasonable to expect that printing ink manufacturers will require ever more effective milling machines to make their own products. Milling manufacturers will undoubtedly find many different ways to meet those needs.